The invention relates to a machine for machining workpieces including a rotary drive with a mounting for a rotary element, namely a tool or a workpiece, and at least a feed drive for converting a relative movement between tool and workpiece. The invention further relates to a compensation unit for such a machine as well as to a process for machining workpieces.
Such machines are for example milling machines with rotating cutter head, drilling machines, grinding machines and the like, but also lathes.
Heretofore, these machines are configured in the form of numerically controlled (CNC) automated manufacturing machines and attain a very high degree of precision as a consequence of the highly accurate mechanical configuration of the automated machine as well as the ingenious control and regulating methods that enable to mill even complicated structures by means of a relative small cutter head so that the need for a tool exchange is eliminated and the shut-down period of the automated manufacturing machine is thus reduced.
In order to meet the demanded high standard of quality, the production process requires to substantially prevent or eliminate all error sources that may impair the production result. One error source that may adversely affect the production process is for example the imbalance of a turning tool, such as cutter head, or of a turning workpiece such as a shaft being worked on, or the like.
For example, an imbalance of a turning cutter head may result, depending on the extent of the imbalance and the rotating speed, in a deflection of the cutter head in circumferential direction so that the cutter head exhibits a greater milling circumference as intended. Although this may be countered by employing highly-precise (balanced) cutter heads and by re-adjusting the mounting of the cutter head, the imbalance can, however, never be completely avoided. Furthermore, an imbalance of the cutter head or of the mounting may be caused by damages or wear, necessitating a premature replacement of the tool or a readjustment. Both procedures are relatively expensive and complicated.
Imbalances adversely affect also rotary workpieces. An imbalance of for example rapidly turning rotary bodies such as shafts or the like may lead to a premature wear of bearings. Typically, such structural elements are therefore subjected to a balancing procedure.
Such a balancing procedure is effected by clamping the rotary part in a balancing device and caused to rotate, with the size and position (rotational disposition) of possible imbalances being registered by imbalance sensors, e.g. force sensors on the bearing. Subsequently, the rotary part is decelerated, and material is either removed or applied at the location constituting the imbalance; It is also possible to compensate the imbalance by removing material at one site and depositing material on another site. These procedures are repeated, i.e. the rotary part is again rotated for determining any imbalance and subsequently decelerated for compensating the imbalance until the resultant imbalance falls below a tolerable limit. However, these treatment procedures, too, are complicated and time consuming.